In recent years, the remote WAN (Wide Area Network) service has come to use LAN (Local Area Network) techniques such as Ethernet (registered trademark). In the WAN service, however, the maintenance and operation of the WAN functions are not sufficient.
In view of this, the telecommunication common carriers often carry out maintenance and operations using the TCP/IP management protocol SNMP (Simple Network Management Protocol).
With SNMP, however, the states up to layer 2 cannot be judged, and in order to secure a high reliability of maintenance and operation, the capability of judgment up to the state of layer 2 is desired.
Under the circumstances, the OAM is being standardized as Y.1731 of ITU (International Telecommunication Union)-T or IEEE802. lag of IEEE (Institute of Electrical and Electronic Engineers).
The OAM is a protocol technique used for maintenance and operation of a network device, and by use of this protocol technique, a fault which may occur may be automatically detected and the place of the fault may be analyzed.
In the packet transmission apparatus employing the OAM to transmit and receive user flows containing the OAM packets and the communication packets, policing is carried out, upon receipt of the user flow, based on the user flow monitor rate regardless of whether the packets are communication packets or OAM packets.
Policing is equivalent to a rate limiting function which controls the transparent output of a user flow containing communication packets and OAM packets based on the monitor rate setting.
In the packet transmission apparatus, assume that policing is carried out on the user flow. When the user flow transmission rate exceeds the monitor rate, the packets in the particular user flow are discarded. When the user flow transmission rate has yet to exceed the monitor rate, on the other hand, the packets in the particular user flow are transparently output.
Also, in the packet transmission apparatus, the communication packets and the OAM packets are extracted from the user flow after policing, and the OAM packets are transmitted to a CPU through a buffer.